Erosion rates and weathering timescales in the eastern Great Escarpment, South Africa

2021 ◽  
pp. 120368
Author(s):  
Tebogo V. Makhubela ◽  
Jan D. Kramers ◽  
Sibusiso M. Konyana ◽  
Herman S. van Niekerk ◽  
Stephan R. Winkler
Keyword(s):  
South Africa ◽  
Erosion Rates ◽  
Great Escarpment

scholarly journals Rich sister, poor cousin: Plant diversity and endemism in the Great Winterberg–Amatholes (Great Escarpment, Eastern Cape, South Africa)

2014 ◽  
Vol 92 ◽  
pp. 159-174 ◽  
Author(s):  
V.R. Clark ◽  
A.P. Dold ◽  
C. McMaster ◽  
G. McGregor ◽  
C. Bredenkamp ◽  
...  
Keyword(s):  
South Africa ◽  
Plant Diversity ◽  
Eastern Cape ◽  
Great Escarpment

Aloe ×gemmelliae (Asphodelaceae subfam. Alooideae), a new natural hybrid between A. broomii and A. grandidentata from the southwestern Free State province, South Africa

Phytotaxa ◽  
2019 ◽  
Vol 423 (3) ◽  
pp. 182-186
Author(s):  
GIDEON F. SMITH ◽  
ESTRELA FIGUEIREDO
Keyword(s):  
South Africa ◽  
Free State ◽  
Natural Hybrid ◽  
Free State Province ◽  
Great Escarpment

Although most species of Aloe Linnaeus (1753: 319) flower in winter, the comparatively few taxa of this genus that occur naturally above South Africa’s climatically severe Great Escarpment tend to flower during spring when temperatures are on the increase. Two such species are A. broomii Schönland (1907: 137) and A. grandidentata Salm-Dyck (1822: 3 [species no. 2]).

Spatial variation of erosion rates and passive margin escarpment embayment from New England, NSW and Bellenden Ker, Queensland, Australia: an analysis using GIS and in-situ 10Be basin-wide cosmogenic nuclides

2020 ◽  
Author(s):  
Jamie Glass ◽  
Alexandru Codilean ◽  
Reka Fülöp ◽  
Klaus Wilcken ◽  
Tim Cohen ◽  
...  
Keyword(s):  
New England ◽  
Spatial Variation ◽  
Erosion Rate ◽  
Soil Depth ◽  
High Elevation ◽  
Passive Margin ◽  
Annual Rainfall ◽  
Main Trunk ◽  
Erosion Rates ◽  
Great Escarpment

<p>The eastern seaboard of Australia is characterized by a passive margin and a continental divide that separates the inland-draining rivers from those that drain to the Coral and Tasman seas. Seaward of this divide lies the Great Escarpment (GE) of Australia that separates a moderate relief coastal plain from a low relief, high elevation plateau. Quantifying the spatial variation of erosion rates from temperate New England (NE), NSW and tropical Bellenden Ker (BK), Queensland, two regions with distinctly different climates and escarpment embayment, could help constrain erosional controls that contribute to escarpment form. In this study, we compared forty detrital 10Be samples collected from sediments in the main trunk and tributaries of five major rivers: the Macleay, Bellinger, and Clarence in NE and the Russel-Mulgrave and North Johnstone in BK. We then traced the escarpment position in ARCGIS and calculated a sinuosity ratio to better compare the degree of embayment in each region. Across both datasets we found that for NE, which has deep gorges cutting into the plateau, the degree of embayment was twice that of BK, where the escarpment position is significantly less embayed and erosion rates significantly more variable (ratio of .18 vs .38). Erosion rates in low slope areas, such as on the plateau, were universally low with no other significant controlling factors. There was no correlation between erosion rates and catchment area, and that our data echo previous studies that find that once mean rainfall passes an approximate threshold (around 2000mm/yr) basin characteristics that are known to control erosion rates, such as slope and lithology, are subdued.</p><p> In temperate NE, where rainfall ranges from approximately 800-1200mm/yr, there was a moderate linear correlation with mean catchment rainfall and erosion rates (R<sup>2</sup> .50), which is likely due to a strong orographic effect due to the escarpment. Erosion rates from tributaries below the plateau were highly variable and ranged from 5m/Ma up to 60m/Ma and correlated strongly with mean catchment slope (R<sup>2</sup> .86). In addition, there were moderate inverse linear correlations between erosion rate and the catchment total percent granite and sedimentary rock (R<sup>2</sup> .53 and .63 respectively) and a moderate correlation between erosion rate and catchment total percent metamorphic rock (R<sup>2</sup> .57). Similar to previous studies, these data suggest that in temperate climates with moderate amounts of annual rainfall, individual basin characteristics play a significant role in controlling basin wide erosion rates.</p><p>In contrast, data from tropical BK, where mean rainfall amounts are in excess of 2000mm/yr, erosion rates from tributaries below the plateau were significantly less variable than NE. Rates had a mean of 37m/Ma ± 9 (standard deviation 5m/Ma, N=10) and were not significantly correlated with mean catchment slope nor catchment lithology. The mean erosion rate of BK is similar to that of other studies in the region, though with slightly less variability, and possibly reinforces the hypothesis from other researchers that in tropical climates with significant mean rainfall, soil depth effectively armors hillslopes and prevents bedrock erosion from occurring.</p>

scholarly journals In quest of contact: phylogeography of helmeted terrapins (Pelomedusa galeata, P. subrufa sensu stricto)

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4901 ◽  
Author(s):  
Melita Vamberger ◽  
Margaretha D. Hofmeyr ◽  
Flora Ihlow ◽  
Uwe Fritz
Keyword(s):  
South Africa ◽  
Distinct Species ◽  
Sensu Stricto ◽  
Western Cape ◽  
Nuclear Markers ◽  
Contact Zones ◽  
Wilderness Area ◽  
General Rules ◽  
Genetic Clusters ◽  
Great Escarpment

Based on rangewide sampling and three mitochondrial and two nuclear markers (together up to 1,850 bp and 1,840 bp, respectively), we examine the phylogeography of two helmeted terrapin species (Pelomedusa galeata and P. subrufa sensu stricto) and infer shifts of climatically suitable spaces since the Last Glacial Maximum using a modeling approach. Whilst P. galeata displays significant phylogeographic structuring across its range and consists of two deeply divergent lineages that could represent distinct species, P. subrufa shows no obvious phylogeographic differentiation. This seems to be related to historically stable or fluctuating ranges. One of the lineages within P. galeata appears to be confined to the westernmost, winter-rainfall region of South Africa and deserves special conservational attention due to the scarcity of surface water. The other lineage is distributed further east and is differentiated in three weakly supported subclades with parapatric distribution; one occurring inland, and two along the south and east coasts, respectively. As far as is known, P. subrufa occurs in South Africa only in the northeast of the country (Limpopo, Mpumalanga) and we report the species for the first time from the Lapalala Wilderness Area in the Waterberg region (Limpopo), approximately 350 km further west than previously recorded. We confirmed the occurrence of P. galeata only 80 km south of Lapalala. Thus, a sympatric occurrence of P. galeata and P. subrufa is possible. Another putative contact zone, for the two lineages within P. galeata, must be located in the Western Cape region, and further contact zones are likely for the eastern subclades within P. galeata. The nuclear loci provided no evidence for gene flow across taxa or genetic clusters within taxa. Future investigations should use denser sampling from putative contact zones and more nuclear markers to re-examine this situation. Despite few phylogeographic studies published for southern African biota, it seems likely that differentiation follows general rules, and that climate and physiographic barriers (e.g., the Great Escarpment) have shaped phylogeographic patterns.

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